Porous crystalline metal oxides are normally synthesized using templating techniques, which are generally categorized into the soft or hard template method depending on the nature of the templates used. For the soft template method, surfactants or amphiphilic block copolymers are employed as structure-directing agents. Since surfactants cannot sustain high temperature, prolonged high-temperature heat treatment cannot be applied and the obtained metal oxides are amorphous or semi-crystalline. The hard templating method for preparing mesoporous oxides was developed to overcome the problems associated with the soft templating method. In hard templating method, inorganic precursors are impregnated into pre-formed ordered mesoporous silica or carbon template and heated at elevated temperatures to obtain crystalline oxide without structural collapse. However, this method of production of mesoporous oxides is still far from commercialization as the initial templates used, i.e. SBA-15, KIT-6, CMK-3 are very expensive and overall synthetic process is capital-expensive. Thus, it is of utmost importance to develop new, efficient synthetic strategies to produce high quality, crystalline mesoporous metal oxides economically at a large scale.
Recently, solution combustion synthesis (SCS) has become a popular method to mass produce nanosize crystalline metal oxides in an energy and time efficient manner. High temperature required for crystals nucleation is achieved by the self-generated heat. Moreover, rapid cooling (typically a few seconds) does not provide sufficient time for extended crystal growth, leading to nanoscale crystals. Despite the many advantages of SCS, commercialization is discouraged by the poor control of porous structure in the metal oxides produced.